A support arm having a self-weight compensation function to attain a balance with a force of gravity acting on the arm is conventionally known. For such a device, Japanese Patent Laying-Open No. 2003-181789, for example, discloses a mechanical self-weight compensation device intended to attain, with a simple structure, a balance with the force of gravity on an actuating arm with respect to orthogonal three axes in space (PTL 1). PTL 1 presents a device (FIG. 6) in which upper and lower two arms constitute a parallel link as a conventional mechanism.
Japanese Patent Laying-Open No. 9-296856 discloses a manipulator intended to achieve a smaller weight and a higher output of a drive source (PTL 2). The manipulator disclosed in PTL 2 has a first arm attached to a frame via a first joint so as to be able to swing, a second arm supported by the leading end of the first arm via a second joint so as to be able to swing, and a gripper for holding a work, the gripper being mounted on the leading end of the second arm. The first arm arranged between the first joint and the second joint is formed by a pair of link members constituting a parallelogram link.